U.S. patent number 4,820,767 [Application Number 06/674,400] was granted by the patent office on 1989-04-11 for process for the production of poly(vinyl acetate) and poly(vinyl alcohol).
This patent grant is currently assigned to Allied-Signal Inc.. Invention is credited to Tse C. Wu.
United States Patent |
4,820,767 |
Wu |
April 11, 1989 |
Process for the production of poly(vinyl acetate) and poly(vinyl
alcohol)
Abstract
This invention relates to a process for the production of
poly(vinyl alcohol) having a weight average molecular weight of at
least about 0.4.times.10.sup.6 by polymerizing vinyl acetate at a
temperature of from about 0.degree. C. to about 40.degree. C. in
the presence of an azo free radical polymerization initiator
essentially in the absence of ultraviolet radiation to form an
essentially linear poly(vinyl acetate) having a weight average
molecular weight of at least about 1.0.times.10.sup.6 and
thereafter hydrolyzing the poly(vinyl acetate) to form the desired
poly(vinyl alcohol).
Inventors: |
Wu; Tse C. (Morristown,
NJ) |
Assignee: |
Allied-Signal Inc. (Morris
Township, NJ)
|
Family
ID: |
24706443 |
Appl.
No.: |
06/674,400 |
Filed: |
November 23, 1984 |
Current U.S.
Class: |
525/62; 525/56;
526/218.1; 526/219; 526/319; 526/330 |
Current CPC
Class: |
C08F
8/12 (20130101); C08F 8/12 (20130101); C08F
118/08 (20130101) |
Current International
Class: |
C08F
8/12 (20060101); C08F 8/00 (20060101); C08F
008/00 () |
Field of
Search: |
;526/319,218.1,330,219
;525/56,62 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
663529 |
|
May 1963 |
|
CA |
|
0712823 |
|
Jan 1980 |
|
SU |
|
900571 |
|
Jul 1962 |
|
GB |
|
2105354 |
|
Mar 1983 |
|
GB |
|
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Reddick; J. M.
Attorney, Agent or Firm: Stewart; Richard C. Fuchs; Gerhard
H.
Claims
What is claimed is:
1. A bulk polymerization process for producing poly(vinylacetate)
which comprises polymerizing vinyl acetate essentially in the
absence of ionizing radiation at a temperature in the range of from
about 0.degree. to about 40.degree. C., and in the presence of from
about 1.times.10.sup.-6 to about 1.times.10.sup.-3 mole percent of
an initiator based on the total moles of vinyl acetate monomer,
said initiator of the formula:
wherein: R.sub.1 and R.sub.2 are the same or different and are
straight or branched chain lower alkyl, lower alkoxyalkyl,
cycloalkyl, nitrile substituted alkyl, or phenylalkylnitrile, for a
time sufficient to provide essentially linear poly(vinylacetate)
having an average molecular weight of at least about
1.0.times.10.sup.6.
2. A process according to claim 1 wherein said process further
comprises hydrolyzing said poly(vinyl acetate) to provide the
corresponding poly(vinyl alcohol), which upon acetylation provides
a poly(vinyl acetate) having an intrinsic viscosity of at least
about 3.3 dL/g.
3. A process according to claim 1 wherein said process is carried
out at a temperature of from about 10.degree. C. to about
35.degree. C.
4. A process according to claim 3 wherein said process is carried
out at a temperature of from about 15.degree. C. to about
30.degree. C.
5. A process according to claim 1 wherein said effective initiator
is an azo compound having a half life of up to about 200 h at a
temperature of from about 0.degree. C. to about 40.degree. C.
6. A process according to claim 5 wherein said effective initiator
is an azo compound having a half life of from about 1 h to about
200 h at a temperature of from about 0.degree. C. at about
40.degree. C.
7. A process according to claim 6 wherein said initiator is an azo
compound having a half life of from about 10 to about 150 h at a
temperature of from about 10.degree. C. to about 35.degree. C.
8. A process according to claim 7 wherein said initiator is an azo
compound having a half life of from about 50 to about 100 hours at
a temperature of from about 15.degree. C. to about 30.degree.
C.
9. A process according to claim 1 wherein said initiator is
2,2-azobis-(2,4-dimethyl-4-methoxyvaleronitrile.
10. A process according to claim 1 wherein the concentration of
said initiator is from about 1.times.10.sup.-6 to about
1.times.10.sup.-3 mole percent based on the total moles of vinyl
acetate monomer.
11. A process according to claim 1 wherein said mole percent is
from about 1.times.10.sup.-5 to about 1.times.10.sup.-3.
12. A process according to claim 11 wherein said mole percent is
from about 2.times.10.sup.-5 to about 2.times.10.sup.-4.
13. A process according to claim 12 wherein said mole percent is
from about 5.times.10.sup.-5 to about 5.times.10.sup.-4.
14. A process according to claim 4 wherein said polymerization is
carried out for a time period of from about 2 to about 48
hours.
15. A process according to claim 14 wherein said time period is
from about 4 to about 36 hr.
16. A process according to claim 15 wherein said time period is
from about 6 to about 24 hr.
17. A process according to claim 16 wherein said time period is
from about 6 to about 18 hours.
18. A bulk polymerization process for producing high molecular
weight poly(vinyl alcohol) which comprises the steps of:
(a) polymerizing vinyl acetate monomer essentially in the absence
of ionizing radiation at a temperature in the range of from about
0.degree. C. to about 40.degree. C. in the presence of from about
1.times.10.sup.-6 to about 1.times.10.sup.-3 mole percent of an
initiator based on the total moles of vinyl acetate monomer, said
initiator of the formula:
wherein: R.sub.1 and R.sub.2 are the same or different and are
straight or branched chain lower alkyl, lower alkoxyalkyl,
cycloalkyl, nitrite substituted alkyl or phenylalkyl, for a time
sufficient to provide an essentially linear poly (vinyl acetate)
having a weight average molecular weight of at least about
1.0.times.10.sup.6 ; and
(b) subjecting said poly(vinyl acetate) to alcoholysis or
hydrolysis to provide the corresponding poly(vinyl alcohol) having
a weight average molecular weight of at least about
0.4.times.10.sup.6.
19. A process according to claim 18 wherein the weight average
molecular weight of said poly(vinyl acetate) is from about
1.3.times.10.sup.6 to about 1.6.times.10.sup.6, and the weight
average molecular weight of said corresponding poly(vinyl alcohol)
is from about 0.5.times.10.sup.6 to about 0.8.times.10.sup.6.
Description
DESCRIPTION
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the polymerization of vinyl acetate to
from poly(vinyl acetate), and the production therefrom of
poly(vinyl alcohol). More particularly, this invention relates to
such a process for the production of poly(vinyl acetate) and
poly(vinyl alcohol) of high molecular weight.
2. Prior Art
Poly(vinyl alcohol) is useful for many purposes. For example,
poly(vinyl alcohol) of especially high viscosity is used as
thickening agent, protective colloid and the like in which high
viscosity solutions having low solid content are desired. Moreover,
poly(vinyl alcohol) is used in textile and paper sizing, in
adhesives, as an emulsion polymerization aid, and as an
intermediate in the production of poly(vinyl butyral), the adhesive
interlayer in laminated safety glass. Furthermore, poly(vinyl
alcohol) is used for textile fiber after
water-insolubilization.
High molecular weight poly(vinyl alcohol) is a high-melting,
high-strength material which is suitable for a wide variety of
applications including tire cord, housing materials, automotive
plastics, super strength fibers, and the like. The excellent
adhesive properties of poly(vinyl alcohol) render it potentially an
outstanding tire cord material.
Poly(vinyl alcohol) is conventionally produced in a two-step
process. In the first step of the process, vinyl acetate is
polymerized to produce poly(vinyl acetate). In the second step, the
poly(vinyl acetate) is subjected to alcoholysis (methanolysis or
ethanolysis) in order to convert the poly(vinyl acetate) to
poly(vinyl alcohol).
Several methods have been proposed for the manufacture of
poly(vinyl alcohol) of relatively high molecular weight. For
example, Canadian Pat. No. 663,529 discloses an emulsification
process for producing poly(vinyl alcohol) in which a vinyl acetate
emulsion is formed, and polymerization is initiated by irradiating
the emulsion in the absence of oxygen with ionizing radiation to a
total radiation dose in the range of 1.20.times.10.sup.4 roentgens
to 2.32.times.10.sup.4 roentgens at a temperature of from
50.degree. C. to -15.degree. C. to form an essentially linear
poly(vinyl acetate) having an intrinsic viscosity of 1.7 to 3.2
dL/g.
Based upon numerical calculation, the poly(vinyl acetate) of
Canadian Pat. No. 663,529 has a viscosity average molecular weight
ranging from about 640,00 to about 1,500,000. Alcoholysis of the
poly(vinyl acetate) of Canadian Patent No. 663,529 would produce
poly(vinyl alcohol) having a viscosity average molecular weight
ranging from about 327,000 to about 765,000.
A similar radiation initiated bulk polymerization procedure is
described in United Kingdom Pat. No. 900,571. In this patent, vinyl
acetate is polymerized by subjecting it to ionizing radiation in
the absence of oxygen or other reactive substances at a temperature
below the temperature at which thermal polymerization of the vinyl
acetate occurs. The resulting poly(vinyl acetate) is hydrolyzed to
produce the desired poly(vinyl alcohol). United Kingdom Pat. No.
900,571 discloses that the poly(vinyl alcohol) produced by the
process of that patent has the molecular structure: ##STR1## where
n is the average degree of polymerization with n being 4,700. The
poly(vinyl alcohol) of United Kingdom Pat. No. 900,571 has a
viscosity average molecular weight of about 200,000, and the
corresponding poly(vinyl acetate) of United Kingdom Pat. No.
900,571 has a viscosity average molecular weight of about
404,000.
Some investigators indicate that production of essentially linear
poly(vinyl acetate) requires a polymerization temperature below
about -15.degree. C. Atkinson, et al., European Polymer Journal,
Vol. 15. pp 21-26 (1979); Hobbs, et al., Journal of Polymer
Science, Vol. XXII, pp. 123-135, 124 (1956); Burnett, et al.,
Journal of Polymer Science, Vol. XVI, pp. 31-44, 39 (1955). Hobbs,
et al. disclose at page 125 the preparation of an essentially
linear poly(vinyl acetate) having an intrinsic viscosity of 3.11.
In order to produce this polymer, Hobbs, et al. employed
azobisisobutyronitrile as an initiator at a concentration of
2.33.times.10.sup.-4 moles per liter and allowed the polymerization
to continue for 37.5 hours at a temperature of -19.degree. C.
Burnett, et al. found that a polymerization temperature of
-25.degree. C. to -38.degree. C. could be employed in order to
obtain essentially linear poly(vinyl acetate). However, Burnett, et
al. noted that polymers prepared at -38.degree. C. had essentially
the same molecular shape as those prepared at -25.degree. C. A
contrary view is that the polymerization temperature is irrelevant
and that essentially linear poly(vinyl acetate) may be obtained as
long as the polymerization is not allowed to proceed to high
conversions of the monomeric vinyl acetate. Matsumoto, et al.,
Journal of Polymer Science, Vol. XLVI pp. 520-523 (1960).
U.S. Pat. No. 4,463,138 discloses that poly(vinyl acetate) can be
produced by free radical bulk polymerization of vinyl acetate with
controlled low initiator concentrations and with ultraviolet
radiation to activate the initiator, employing a polymerization
temperature of between about -25.degree. C. and about -45.degree.
C. for a period of time between about 24 hours and 120 hours. This
patent discloses that the poly(vinyl alcohol) can be prepared by
conventional alcoholysis of the poly(vinyl acetate). Poly(vinyl
alcohol) prepared in accordance with the process has an intrinsic
viscosity greater than about 5 dL/g.
United Kingdom Pat. No. 2,105,354 discloses a process in which
ethylene and vinyl acetate are continuously copolymerized in a
solvent in the presence of a radical initiator whose half life
measured at 60.degree. C. is not longer than 2 hours, such as
2,2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile), at a temperature
in excess of 50.degree. C. The patent states that use of such
inhibitors reduces gel formation.
SUMMARY OF THE INVENTION
The present invention is directed to a bulk polymerization process
of preparing essentially linear poly(vinyl acetate) of high
molecular weight which can be subjected to alcoholysis to provide a
high molecular weight poly(vinyl alcohol). More particularly, this
invention provides an improved bulk polymerization process in which
the polymerization of vinyl acetate is initiated by an "initiating
effective amount" of an "effective initiatior", preferably an azo
initiator having a half life of from about 500 to about 3 hours
measured at a temperature of from about 0.degree. C. to about
40.degree. C. substantially in the absence of ultra-violet
radiation. The process is carried out at a temperature of from
about 0.degree. C. to about 40.degree. C. This invention also
relates to high molecular weight essentially linear poly(vinyl
acetate) and high molecular weight poly(vinyl alcohol) produced via
alcoholysis of said poly(vinyl acetate).
In its simplest form, poly(vinyl acetate) may be represented as
follows by structure I: ##STR2## wherein n is the degree of
polymerization (i.e. number of repeat units). Upon alcoholysis,
structure I is converted to poly(vinyl alcohol) which may be
represented as follows by structure II: ##STR3## wherein n is as
described for structure I.
It should be appreciated, however, that poly(vinyl acetate) having
a structure corresponding to structure I is most difficult to
obtain by bulk polymerization procedures. The difficulty is
associated with the fact that during vinyl acetate polymerization,
a hydrogen may be abstracted from the alpha, beta or methyl carbon
of the acetate group to produce radical sites capable of combining
with other vinyl acetate monomers to form a chain. Such
combinations result in poly(vinyl acetate) which contains extended
branches and, of course, is nonlinear. Branching at the alpha and
beta carbons is known to occur much less frequently than branching
at the methyl carbon of the acetate group, and such branching is
not considered a major problem. However, branching at the methyl
group of the acetate group is somewhat common under certain
conditions and will/may lead to poly(vinyl acetate) having a
significant number of branch points according to structure III
which is as follows: ##STR4## Even worse, the branching mechanism
may continue further to produce branch points represented by
structure IV as follows: ##STR5## wherein X is CH.sub.3
(termination of branching) or --CH.sub.2 -- (further branching) and
m is an integer. In structures III, and IV above, n is as
previously described hereinabove, and a is the number of unbranched
repeat units.
The occurrence of substantial branching during vinyl acetate
polymerization is most undesirable if one desires to convert the
poly(vinyl acetate) to poly(vinyl alcohol). In order to appreciate
the undesirability of substantial branching, one must first
appreciate that upon alcoholysis of poly(vinyl acetate) for the
production of poly(vinyl alcohol), the acetate groups are cleaved
from the backbone of the polymer. Thus, the molecular weight of
poly(vinyl alcohol) will necessarily be about one half that of
poly(vinyl acetate) due to the molecular weight of the repeat units
for each polymer. The molecular weight of a poly(vinyl acetate)
repeat unit is about 86, while the repeat unit of poly(vinyl
alcohol) has a molecular weight of about 44. However, if a
significant number of the acetate groups have attained greater
length (i.e. greater molecular weight) via a branching mechanism,
the poly(vinyl alcohol) produced by alcoholysis of the
significantly branched poly(vinyl acetate) will have a molecular
weight significantly less than one half the molecular weight of the
poly(vinyl acetate). Therefore, in order to produce high molecular
weight poly(vinyl alcohol), it is necessary that the number of
extended branches contained by the precursor polymer, poly(vinyl
acetate), be minimized as much as possible.
While the process described in U.S. Pat. No. 4,463,138 minimizes
the formation of extended branches to a significant extent, and
provides excellent ultra-high molecular weight poly(vinyl alcohol)
and poly(vinyl acetate), it does suffer from a number of inherent
disadvantages. For example, the use of radiation and the lower
reaction temperatures require the use of expensive equipment.
Surprisingly, we have discovered that an essentially linear, high
molecular weight poly(vinyl acetate) can be produced (which would
be described in more detail below) by using certain initiators
substantially without activation by ultraviolet light at certain
temperatures. The poly(vinyl acetate) can be conventionally
hydrolyzed using conventional procedures to provide high molecular
weight poly(vinyl alcohol). The process of this invention not only
eliminates the need for costly equipment, but also allows the
polymerization to be carried out at or near ambient temperatures.
Moreover, this process provides high molecular weight poly(vinyl
alcohol) which can be conveniently used for applications where
poly(vinyl alcohol) having high melting point and high strength are
required.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of this invention consists of two essential steps. The
first step of the process can be depicted schematically as follows:
##STR6## wherein n is an integer of from about 2500 to 25,000,
preferably from about 9000 to about 23,000, and most preferably
from about 11,000 to about 21,000. The first step of the process of
this invention can be conveniently carried out by bulk polymerizing
vinyl acetate in the presence of an "initiating effective amount"
of an "effective initiator" at an "effective temperature" for a
period sufficient to form the desired poly(vinyl acetate).
As used herein, an "effective initiator" is a free radical
polymerization initiator which is capable of bulk polymerizing
vinyl acetate at a temperature of from about 0.degree. C. to about
40.degree. C. to provide an essentially linear poly(vinyl acetate)
having a weight average molecular weight equal to or greater than
about 900,000, which on alcoholysis provides a poly(vinyl alcohol)
having a weight average molecular weight equal to or greater than
about 450,000. The weight average molecular weight is determined by
the method described in W. S. Park, et al, Journal of Polymer
Science, Polymer Physics Ed. vol. 15, p. 81 (1977). Usually, the
effective initiator is an azo compound having a half life of up to
about 200 h at a temperature of from about 0.degree. C. to about
40.degree. C. In the preferred embodiments of the invention, the
initiator will have a half life of from about 1 to about 200 hours
at a temperature of from about 0.degree. C. to about 40.degree. C.,
and in the particularly preferred embodiments of the invention, the
initiator of choice will have a half life of from about 10 to about
150 hours at a temperature of from about 10.degree. C. to about
35.degree. C. Amongst these particularly preferred embodiments,
most preferred are those embodiments in which the initiator has a
half life of from about 50 to about 100 hours measured at a
temperature of from about 15.degree. C. to about 30.degree. C. The
half life of the initiator can be calculated from the decomposition
rate of the initiator which is described in, for example, the
"Polymer Handbook", J. Brandrup & E. H. Immergut, John Wiley
& Sons. 1975. Illustrative of initiators suitable for use in
the procedure of the invention are azo compounds of the
formula:
wherein R.sub.1 and R.sub.2 are the same or different, and are
independently straight or branched-chain lower alkyl, lower
alkoxyalkyl, cycloalkyl, nitrile substituted alkyl groups,
phenylalkylnitrile. The selection of suitable R.sub.1 and R.sub.2
groups is well within the skill of the art. Within the scope of the
above formula preferred azo initiator are
2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile); 2,2'-azobis
2,4-dimethylvaleronitrile); 1,1'-azobis-1-cyclooctanenitrile;
azobis-2-methylbutyronitrile;
1,1'-azobis-1-cyclohexanecarbonitrile;
2,2'-azobis-2-propylbutyronitrile;
2,2'-azobis-2-methylhexylonitrile;
2,2'-azobis-2-benzylpropionitrile and the like. Amongst these
preferred initiators,
2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile) is most
preferred.
There is a relationship between the amount initiator employed, the
polymerization temperature and polymerization times. Each of the
aforementioned process parameters are selected to maximize the
molecular weight of the poly(vinyl acetate), and to minimize the
degree of branching. In general, acceptable results are provided
when the initiator concentration varies from about
1.times.10.sup.-6 to about 1.times.10.sup.-3 mole percent based on
the total moles of vinyl acetate monomer, the polymerization
temperature is from about 0.degree. C. to about 40.degree. C., and
polymerization times are from about 2 to about 48 h. In the
preferred embodiments of the invention, initiator concentrations
will vary from about 1.times.10.sup.-5 to about 1.times.10.sup.-3
mole percent on the aforementioned basis, polymerization
temperatures will vary from about 10.degree. C. to about 35.degree.
C., and polymerization times will vary from about 4 to about 36 h.
In the particularly preferred embodiments, initiator concentrations
will vary from about 2.times.10.sup.-5 to about 2.times.10.sup. -4
mole percent on the aforementioned basis, polymerization
temperatures will vary from 15.degree. C. to about 25.degree. C.,
and polymerization times will vary from about 6 to about 24 h.
Amongst these particularly preferred embodiments most preferred are
those embodiments, in which initiator concentration is from about
5.times.10.sup.-5 to about 5.times.10.sup.-4 mole percent on the
aforementioned basis, polymerization temperatures are in the range
of from about 15.degree. C. to about 25.degree. C. and
polymerization times are from about 6 to about 18 h.
In the process of this invention for the production of high
molecular weight essentially linear poly(vinyl acetate) the
starting material, the vinyl acetate monomer preferably has a
purity equal to or greater than about 99% by weight and most
preferably equal to or greater than about 99.9% by weight . Small
scale quantities of vinyl acetate having a purity equal to or
greater than about 99.9% by weight may be obtained by fractionating
vinyl acetate monomer with a 200-plate spinning band column and
collecting the middle boiling fraction to about 72.2.degree. C.
Large quantities of vinyl acetate having a purity equal to or
greater than 99.9% by weight for industrial production of high
molecular weight poly(vinyl alcohol) may be obtained by standard
industrial distillation procedures which are well known to those
having skill in the art.
Polymerization of the vinyl acetate monomer is accomplished by
initiated radical polymerization. Oxygen acts as an inhibitor of
radical polymerization and, accordingly the polymerization is
preferably carried out under substantially oxygen free condition.
Thus, the fractionated highly pure vinyl acetate monomer is
preferredly subjected to deoxygenation procedures prior to
polymerization. This may be accomplished by a freeze-thaw operation
under a high vacuum and an inert gas sweep wherein the monomer is
frozen at about -93.degree. C., thawed, refrozen, thawed, etc. The
vinyl acetate monomer should undergo at least about three
freeze-thaw cycles in order to ensure an essentially complete
removal of oxygen. However, removal of oxygen by bubbling pure
nitrogen through the polymerization mixture is also adequate in
this invention.
Once a purified and deoxygenated vinyl acetate monomer is obtained,
the monomer may then be transferred to a suitable reactor for
conducting the free radical bulk polymerization process of this
invention. Reactors suitable for use in the polymerizing reaction
are not critical, and reactors used in conventional bulk
polymerizations can be used. Suitable reactors will usually be
equipped with a temperature control means to maintain the reaction
mixture within the desired temperature range, and should also be
equipped with means to maintain the reactor substantially oxygen
free; as for example, means for carrying out the polymerization
under an inert gas such as nitrogen.
The process of this invention can be conducted in a batch,
semicontinuous or continuous fashion. The reaction can be conducted
in a single reaction zone or in a plurality of reaction zones, in
series or in paralleled or it may be conducted intermittently or
continuously in an elongated tubular zone or series of such zones.
The materials of construction employed should be inert to the
reactants during the reaction and the fabrication of the equipment
should be able to withstand the reaction temperatures and
pressure.
The reaction zone can be fitted with one or more internal and/or
external heat exchanger(s) in order to control undue temperature
fluctuations, or to prevent any possible "runaway" reaction
temperatures or fluctuations therein. In preferred embodiments of
the process, agitation means to vary the degree of mixing of the
reaction mixture can be employed. Mixing by vibration, shaking,
stirring, rotation, oscillation, ultrasonic vibration or the like
are all illustrative of the type of agitation means contemplated.
Such means are available and well known to those skilled in the
art.
The reactants and reagents may be initially introduced into the
reaction zone batchwise or may be continuously or intermittently
introduced in such zone during the course of the process. Means to
introduce and/or adjust the quantity of reactants introduced,
either intermittently or continuously into the reaction zone during
the course of the reaction, can be conveniently utilized in the
process especially to maintain the desired molar ratio of the
reaction solvent, reactants and reagents.
Upon completion of the polymerization process, unreacted vinyl
acetate may be removed by distillation under atmospheric or
sub-atmospheric pressures. A polymeric residue comprising
poly(vinyl acetate) will remain in the vessel utilized for the
removal of unreacted vinyl acetate. The poly(vinyl acetate) product
may be worked up by conventional means, as for example by initially
dissolving the polymeric residue in an organic solvent such as
acetone, tetrahydrofuran, methanol, dichloromethane, ethyl acetate,
etc., and then precipitating the polymer with a non-solvent such as
hexane, cyclohexanol, diethyl ether, mesitylene or the like.
Similarly, precipitation of the polymers may be accomplished by
simply employing cold water. Recovery of the polymer is then
accomplished by standard filtration and drying procedures.
Poly(vinyl acetate) produced in accordance with this invention has
an intrinsic viscosity, and thus a corresponding molecular weight
which is only slightly higher than reacetylated poly(vinyl acetate)
produced from poly(vinyl alcohol) resulting from alcoholysis of the
original poly(vinyl acetate). Thus, the poly(vinyl acetate)
produced in accordance with this invention is essentially linear.
Poly(vinyl acetate) produced in accordance with the process of this
invention has an intrinsic viscosity which is equal to or greater
than about 3.2 dL/g. This corresponds to a weight average molecular
weight of equal to or greater than about 1.0.times.10.sup.6. Thus,
given the fact that the repeat unit of poly(vinyl acetate) has a
molecular weight of about 86 and the repeat unito of poly(vinyl
alcohol) has a molecular weight of about 44, poly(vinyl alcohol)
produced (by the alcoholysis of such poly(vinyl acetate) has a
weight average molecular weight of at least about
0.45.times.10.sup.6. In the preferred embodiments of this
invention, the poly(vinyl acetate) produced in accordance with the
process of this invention will have an intrinsic viscosity ranging
from about 3.5 dL/g to about 4.0 dL/g. Poly(vinyl acetate) falling
within this intrinsic viscosity range has a weight average
molecular weight ranging from about 1.3.times.10.sup.6 to about
1.6.times.10.sup.6, and poly(vinyl alcohol) pepared by the
alcoholysis of this material will have a weight average molecular
weight ranging from about 0.5.times.10.sup.6 to about
0.8.times.10.sup.6.
The determination of the weight average molecular weight of
poly(vinyl acetate) may be accomplished by any one of a number of
techniques known to those skilled in the art. Illustrative examples
of suitable means for conducting the molecular weight determination
include light scattering techniques which yield a weight average
molecular weight and intrinsic viscosity determination which may be
correlated to weight average molecular weight in accordance with
the relationship [.eta.]=5.1.times.10.sup.-5 M.sup.0.791, described
more fully by W. S. Park, et al. in the Journal of Polymer Science,
Polymer Physics Ed., vol. 15, p. 81 (1977).
The second step of the process of this invention can be depicted
schematically as follows: ##STR7## wherein n is as described above.
Conventional procedures for the alcoholysis of poly(vinyl acetate)
can be used to convert the poly(vinyl acetate) into poly(vinyl
alcohol). Illustrative of such procedures are those described in
detail in U.S. Pat. No. 4,463,138 which is incorporated herein by
reference. Briefly stated, the alcoholysis of step 2 above may be
accomplished by initially dissolving the poly(vinyl acetate) in a
quantity of a low molecular weight alcohol such as methanol or
ethanol sufficient to form at least about a 2% solution of the
poly(vinyl acetate) resin Base or acid catalysis may then be
employed in order to convert the poly(vinyl acetate) to poly(vinyl
alcohol) which is produced in the form of a gel. Base catalysis is
preferred, however, with suitable bases including potassium
hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide,
etc. The gel material is then chopped into small pieces and
extracted repeatedly with methanol, ethanol or water for removal of
residual base salts. The essentially pure poly(vinyl alcohol) is
then dried under vacuum at a temperature of about 30.degree. C. to
about 70.degree. C. for about 2 to 20 hours. Poly(vinyl alcohol)
produced in accordance with the process of this invention will have
a weight average molecular weight of at least about
0.45.times.10.sup.6. In the preferred embodiments, the weight
average molecular weight of the poly(vinyl alcohol) is from about
0.45.times.10.sup.6 to about 1.0.times.10.sup.6 and in the
particularly preferred embodiments is from about 0.5.times.10.sup.6
to about 0.8.times.10.sup.6.
Poly(vinyl alcohol) produced in accordance with this invention is
useful in the production of poly(vinyl alcohol) fibers of excellent
strength. Also, fibers produced from the poly(vinyl alcohol) of
this invention have high melting points. Fibers produced from the
high molecular weight poly(vinyl alcohol) of this invention and
processes for their production are described more fully in commonly
assigned U.S. Pat. No. 4,449,711. Accordingly, such procedures will
not be described herein in detail.
The following examples are presented to more particularly
illustrate the invention, and should not be construed as
limitations thereon.
EXAMPLE I
A solution containing 3.1 mg of ABVN initiator,
(2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile)), and 100 g of
vinyl acetate was placed in a 500 mL 3-necked flask, fitted with a
condenser and a gas dispersion tube. Nitrogen was introduced by
bubbling through the solution for two hours in order to remove air
from the system. The reaction mixture was kept at 21.degree. C. for
18 hours under a blanket of nitrogen.
At the end of this period, the unreacted monomer was evaporated
from the reaction mixture. Methanol was added to the residue and
stirred. A sample of the solution was analyzed and found to have a
molecular weight of 1.53.times.10.sup.6. The methanolic solution
was hydrolyzed in the presence of 1 g of potassium hydroxide which
yielded 11.9 g (23.3% conversion) of poly(vinyl alcohol). A sample
was reacetylated and found to have a molecular weight of
1.8.times.10.sup.6. Thus, it showed that the original poly(vinyl
acetate) was essentially linear.
A 7.5% of the poly(vinyl alcohol) in glycerol at 200.degree. C. was
gel spun into a fiber which was extracted with methanol and then
drawn at 255.degree. C. with an overall draw ratio of 6.9. The
drawn fiber had a tensile strength of 14.2 gpf, ultimate elongation
of 2.7%, and modulus of 630 gpd.
EXAMPLES II TO V
Using the procedure of Example I, vinyl acetate (VAM) was bulk
polymerized in the presence of ABVN initiator to form poly(vinyl
acetate), which was converted to poly(vinyl alcohol). The
polymerization parameters, % conversion of poly(vinyl acetate) into
poly(vinyl alcohol), and intrinsic viscosity and molecular weight
of the poly(vinyl acetate) are set forth in the following Table
I.
TABLE I
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ABVN Time Temp. Conv. I.V. MW VAM Example No. M .times. 10.sup.4
(HR) (.degree.C.) (%) (dL/g) (M .times. 10.sup.6) (g)
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II 1 18 21 23.3 3.93 1.53 100 III 1 18 23 27.8 4.06 1.60 50 IV 2 6
21 10.6 3.41 1.26 50 V 4 6 20 7.4 3.36 1.24 50
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EXAMPLE VI
A solution containing 15.5 mg of
(2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile) and 1000 g of
vinyl acetate was stirred in a 3-necked 2-liter flask placed in a
water bath at 20.degree. C. During this period the solution was
deaerated by bubbling nitrogen through a gas dispersion tube below
the liquid surface for an hour. The dispersion tube was then raised
above the liquid surface so that the reaction mixture was blanketed
by nitrogen throughout the entire polymerization period.
After 18 hours, 1 g of p-methoxyphenol was added. The unreacted
vinyl acetate was distilled from the reaction mixture in a vacuum
at about 50.degree. C. The polymeric residue was dissolved in about
3 liters of methanol at about 50.degree. C. A sample of the
methanolic solution was taken for analysis. The intrinsic viscosity
of the polymer in tetrahydrofuran was found to be 3.72 dL/g. The
weight average molecular weight calculated from the intrinsic
viscosity was 1.40.times.10.sup.6.
The methanolic solution of poly(vinyl acetate) was stirred in the
presence of 4 g of potassium hydroxide at room temperature for
about 2 hours. A gel formed which was chopped up in a blender and
washed twice with methanol. The solids were filtered and dried in a
vacuum oven at 50.degree. C. The poly(vinyl alcohol) thus obtained
weighed 59.4 g. The conversion was about 11.5%.
EXAMPLES VII TO XV
Using the procedure of Example VI, vinyl acetate (VAM) was bulk
polymerized in the presence of
2,2'-azobis-(2,4-dimethyl-4-methoxy-valeronitrie) (ABVN) to form
poly(vinyl acetate), which was converted to poly(vinyl
alcohol).
The polymerization parameters, % conversion of the poly(vinyl
acetate) into poly(vinyl alcohol), and intrinsic viscosity and
molecular weight of the poly(vinyl acetate) are set forth in the
following Table II.
TABLE II
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ABVN Time Temp. Conv. I.V. MW VAM Example No. M .times. 10.sup.4
(HR) (.degree.C.) (%) (dL/g) (M .times. 10.sup.6) (g)
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VII 0.5 18 20 11.5 3.72 1.40 500 VIII 0.9 18 15 4.3 3.61 1.35 500
IX 1 6 20 3.4 3.49 1.30 500 X 1 18 20 11.7 3.57 1.33 500 XI 1 18 20
16.5 3.74 1.41 500 XII 0.25 18 20 3.9 3.57 1.33 1000 XIII 0.5 18 20
11.5 3.72 1.40 1000 XIV 0.5 18 20 10.4 3.67 1.38 1000 XV 4 6 20
10.3 3.43 1.27 1000 XVI 0.5 18 20 16.6 3.73 1.41 1000
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